WCH14 Rates, Equilibria and Further Organic Chemistry

Lessons in WCH14

1. Rate equations, orders and rate constants
   rate = k[A]^m[B]ⁿ. Orders come from experiment, not the equation. Overall order = m + n; it decides the units of k. k changes only with temperature or a cataly
2. Finding orders: graphs, initial rates and half-life
   Rate data come from gas volume, mass, colorimetry, titration or pH. Initial rates: compare runs where one concentration changes. Constant half-life means first
3. Iodine-propanone and clock reactions (Core Practicals 9a and 9b)
   rate = k[CH3COCH3][H+]; zero order in I2, so iodine is not in the slow step. CP9a: quench samples with NaHCO3 and titrate I2 with thiosulfate. CP9b: initial rat
4. Rate-determining steps and mechanisms
   The RDS contains the species in the rate equation. Mechanism steps must add up to the overall equation. Rate = k[RX][OH-] means SN2 (primary); rate = k[RX] mean
5. Activation energy, the Arrhenius equation and catalysts (Core Practical 10)
   ln k = ln A - Ea/RT. Plot ln k (or ln(1/t)) against 1/T: gradient = -Ea/R. Heterogeneous catalysts work by adsorption, bond weakening and desorption at a surfac
6. Entropy and the direction of change
   Entropy is disorder; S rises from solid to liquid to gas. More gas moles means positive ΔSsystem. ΔS°system = ΣS°products - ΣS°reactants; elements do not have z
7. Total entropy change and feasibility
   ΔStotal = ΔSsystem + ΔSsurroundings, with ΔSsurroundings = -ΔH/T (ΔH in J). Feasible when ΔStotal > 0. Feasible is not the same as fast: high Ea gives kinetic s
8. Lattice energy and Born-Haber cycles
   Born-Haber: ΔfH = atomisations + ionisation energies + electron affinities + lattice energy. Small, highly charged ions give more exothermic lattice energies. E
9. Enthalpies of solution and hydration
   ΔsolH = -LE + ΣΔhydH. Hydration is always exothermic, more so for small, highly charged ions. Solubility depends on entropy as well as ΔsolH.
10. Equilibrium constants Kc and Kp
    Kc uses equilibrium concentrations, Kp uses partial pressures (mole fraction x total pressure). Leave out solids. Work out units by cancelling.
11. How conditions affect K, and ΔStotal = R ln K
    Only temperature changes K. Exothermic: K falls as T rises; endothermic: K rises. ΔStotal = R ln K. Very large K means the reaction goes to completion.
12. Brønsted-Lowry acids and the pH scale
    Acid = proton donor, base = proton acceptor; conjugate pairs differ by H+. pH = -log10[H+]. Strong acids dissociate fully, so [H+] = [acid] for HCl.
13. Weak acids, Ka and pKa
    Ka = [H+][A-]/[HA]; pKa = -log Ka. For a weak acid [H+] = √(Ka[HA]), assuming [H+] = [A-] and negligible dissociation.
14. The ionic product of water and the pH of bases
    Kw = [H+][OH-] = 1.00 x 10^-14 mol² dm^-6 at 298 K. For strong bases [H+] = Kw/[OH-]. Neutral means [H+] = [OH-], not always pH 7.
15. pH titration curves and indicators (Core Practical 11)
    Strong acid-strong base: equivalence pH 7. Weak acid-strong base: above 7, phenolphthalein. Strong acid-weak base: below 7, methyl orange. At half-neutralisatio
16. Buffer solutions
    Buffer: weak acid + conjugate base in large amounts. [H+] = Ka[HA]/[A-]. Added H+ is removed by A-, added OH- by HA. Blood uses H2CO3/HCO3-.
17. Optical isomerism and chirality
    Chiral centre: carbon with four different groups. Enantiomers rotate plane-polarised light in opposite directions; a racemic mixture is inactive. SN2 gives an a
18. Aldehydes and ketones: properties, oxidation and reduction
    Aldehydes -CHO, ketones C=O in the chain. No hydrogen bonding between molecules, but soluble through hydrogen bonds with water. Fehling's, Tollens' or dichromat
19. Nucleophilic addition and tests for carbonyl compounds
    CN- adds to the δ+ carbon, then O- picks up H+: a hydroxynitrile. 2,4-DNPH gives an orange precipitate with any C=O compound; melting point of the derivative id
20. Carboxylic acids
    -COOH acids hydrogen bond strongly (high boiling points, small ones soluble). Made by oxidising alcohols or aldehydes, or hydrolysing nitriles. React with LiAlH
21. Acyl chlorides, esters and polyesters
    Acyl chlorides + water/alcohol/ammonia/amine give acid/ester/amide/N-substituted amide plus HCl, fast and irreversibly. Esters: acid hydrolysis is reversible; a
22. Carbon-13 NMR spectroscopy
    One peak per carbon environment; symmetry reduces the number. δ relative to TMS: alkyl 5 to 55, C-O 50 to 90, C=C 110 to 160, C=O 160 to 220.
23. Proton NMR: chemical shift, integration and splitting
    Number of peaks = proton environments. Area = number of H. Splitting by n adjacent non-equivalent H gives n + 1 lines. Ethyl group: quartet + triplet.
24. Chromatography and high-resolution mass spectrometry
    Separation depends on relative affinity for the stationary and mobile phases. Rf = spot distance / solvent front distance. GC and HPLC use retention times; with

Next exams for WCH14

• January 2027: Mon 18 Jan 2027, afternoon, 1h 45m
• Summer 2027: Wed 26 May 2027, afternoon, 1h 45m

From Pearson's final timetables. All exam dates. Always confirm your entries with your exams officer.